1. Technical Field
The present invention relates in general to an improved system for processing wastewater, and in particular to an improved aerobic system and method for processing and managing wastewater effluent.
2. Description of the Related Art
The treatment of wastewater, whether for purposes of recycling or prior to its discharge into treatment works, rivers, lakes, groundwater suppliers, etc., is an ever-increasing problem. To date, three general classes of methods for removing contaminating organic substances from wastewater, such as sewage, have been developed. These are chemical treatments, biological treatments, and physical treatments.
Biological treatments have been used in a wide variety of applications. Generally, the treatment involves contacting wastewater with a consortium (community) of microorganisms that utilize dissolved organic substances as nutrients. During the biological treatment, three main activities occur: reduction of biological oxygen demand (B.O.D reduction), nitrification and denitrification of the organic waste. All three processes are affected by bacteria, the former two—by aerobic bacteria, and the latter—by anaerobic (anoxic) bacteria.
In the various reactors for biological treatment of sewage, mutual disposition of the biological activities in the overall treatment may be different in that the denitrification stage may be performed before, concurrently or after B.O.D. reduction. When denitrification is performed before B.O.D. reduction and nitrification, this may take place either in a separate reactor or in the area of the main reactor where the raw sewage enters. When denitrification is performed after B.O.D. reduction and nitrification, the system typically requires its supplementation with an additional source of carbon, such as methanol, in order to effect denitrification. When denitrification, B.O.D. reduction and nitrification occur concurrently, in a so called combined system, this system typically comprises alternating aerobic and anaerobic stages in which incremental reduction in the organic carbon and nitrogen content of the sewage is accomplished in each stage. This enables the system to maintain the organic carbon after the B.O.D. reduction stages at a sufficient level for denitrification without adding an additional source of carbon. Systems of this type are disclosed, for example, in U.S. Pat. Nos. 3,994,802; 3,945,918; 4,279,753; 4,564,457 and 4,374,730.
Typically, the combined systems for biological treatment of sewage hitherto known are designed to include the use of aeration and/or agitation means during the aerobic stage of the treatment for the purpose of reduction of the time required for nitrification. Nearly all prior art sewage purification systems require that sooner or later the system be closed down to allow removal of sludge that has not been fully treated and has accumulated in the processing vessels. Large municipal treatment plants have the equipment and personnel to carry out this work. However, small-scale systems intended for the use of a single house or housing blocks are better served by arrangements that almost completely dispose of organic solids and so do not require such servicing.
Methods and apparatus for treating domestic effluents are disclosed in U.S. Pat. No. 4,172,034 (Carlsson, et al); U.S. Pat. No. 4,812,237 (Cawley); U.S. Pat. No. 5,114,586 (Humphrey) and U.S. Pat. No. 5,342,523 (Kuwashima). Carlsson describes an apparatus, which operates on an easy-flowing slurry, having a dry solids content of between 1–15%, preferably 5–10%. Such a dilute slurry unnecessarily extends processing time to achieve aerobic degradation in a reaction vessel with aeration; however, the Carlsson apparatus has the advantage of being compact.
Humphrey discloses a complex sanitation system provided with many vessels, five of which have multiple air entry orifices. The resulting high air consumption necessitates the installation of a large air blower or compressor, leading to high running costs and a noise suppression problem. Another difficulty encountered in the Humphrey system is finding space in a residential building for all the described system components.
Cawley describes and claims a process for purifying and recycling household wastewaters, comprising the steps of (a) collecting a first wastewater stream from household kitchen sources; (b) anaerobically digesting said first wastewater stream in a first septic tank; (c) collecting a second wastewater stream from household laundry and bathing sources; (d) combining water from steps (b), (c) and (h); (e) anaerobically digesting water from step (d) in a second septic tank; (f) pumping water from step (e) over a biological sand filter under aerobic conditions; (g) pumping biologically filtered water from step (f) through an ultra-filter, thereby separating the biologically filtered water into a retentate stream and a permeate stream; (h) returning said retentate stream to step (d); (i) disinfecting said permeate stream; (j) returning a first portion of said disinfected permeate stream to household laundry and bathing facilities; (k) separating a second portion of said disinfected permeate stream into a low salt portion and a high salt portion; (l) returning said low salt portion to a household kitchen; and (m) disposing of said high salt portion.
Kuwashima proposes a pair of separator tanks, which are used alternately for separating floating or sedimenting material; the organic material is transferred for aerobic decomposition to a third tank. The device lacks means for breaking up large solids into small particles for efficient decomposition. Although each of these prior art designs are workable, a more effective and efficient means of treating wastewater and sewage would be desirable.